Comparable stake leader
Jack Y. Zhang
SEC ownership of Amphastar Pharmaceuticals, Inc.
Top holders, 13D/G large-stake signals, insider positions, and transaction flow tied to CIK 0001297184.
Disclosed value leader
Jack Y. Zhang
Comparable rows
50/50
Latest evidence
07 Aug 2026
- Public ticker
- AMPH on Nasdaq
- Parsed ownership sources
-
13D/G, 3/4/5, and 13F
Source: Parsed SEC ownership filingsUse: Compare filing families carefully
- Largest SEC-reported holder
-
Jack Y. Zhang
Ranking: Comparable ownership first, then disclosed value
- Comparable ownership rows
-
50 of 50
Meaning: Rows with safely comparable ownership %
- Latest 13D/G holder
-
Jack Y. Zhang
Source: Latest parsed Schedule 13D/G stake
- Latest parsed ownership date
-
07 Aug 2026
Freshness: Most recent filing date in this holder set
- Issuer CIK
- 0001297184
- Issuer location
- Rancho Cucamonga, CA
Ownership snapshot
CIK-linked ownership evidence from parsed SEC filings.
3 signals
Issuer
Names, identifiers, and filing context for this profile.
2 identity fields
Ownership snapshot
Top shareholders of Amphastar Pharmaceuticals, Inc. (13F + 13D/G + 3/4/5)
Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.
Comparable stake leader
Jack Y. Zhang
Disclosed value leader
Jack Y. Zhang
Comparable rows
50/50
Latest evidence
07 Aug 2026
13D/G
3/4/5
13F
Lead comparable stake: 25%
13D/G row: Jack Y. Zhang
Showing 1-8 of 50 holder rows.
Quick read
Jack Y. Zhang leads the comparable SEC ownership view at 25%.
50 of 50 rows have a safely comparable ownership percentage. Use this as a filing-backed starting point, then open the detailed table for source links, reporting role, position value, share count, and filing date.
Open SEC evidence
Opens Jack Y. Zhang's linked filing trail.
Comparable ownership
Top 5
Jack Y. Zhang
25%
BlackRock, Inc.
12%
DIMENSIONAL FUND ADVISORS LP
5.2%
William J. Peters
0.39%
Floyd F. Petersen
0.16%
Ownership % is shown only when SEC disclosures are safely comparable across share classes.
Detailed SEC evidence table Showing 1-8 of 50 holder rows
| Holder | Evidence | Ownership % | Position | 12M Net Δ | As of |
|---|---|---|---|---|---|
| Jack Y. Zhang |
13D/G
3/4/5
CEO & CHIEF SCIENTIFIC OFFICER, Director, 10%+ Owner
|
25%
|
$301,456,363
12,524,153 shares
|
$0 | 31 Dec 2024 |
| BlackRock, Inc. |
13D/G
13F
Company
|
12%
|
$142,136,789
5,333,463 shares
|
$0 | 30 Sep 2025 |
| DIMENSIONAL FUND ADVISORS LP |
13F
13D/G
Company
|
5.2%
from 13D/G
|
$46,519,189
2,305,107 shares
|
— | 30 Jun 2026 |
| William J. Peters |
3/4/5
CFO, EVP & TREASURER, Director
|
0.39%
|
$3,885,578
172,846 shares
|
-$183,886 | 07 Aug 2026 |
| Floyd F. Petersen |
3/4/5
Director
|
0.16%
|
$1,850,044
71,368 shares
|
-$591,072 | 11 Dec 2025 |
| STATE STREET CORP |
13F
Company
|
3.7%
|
$33,138,103
1,642,126 shares
|
— | 30 Jun 2026 |
| VANGUARD CAPITAL MANAGEMENT LLC |
13F
Company
|
3.3%
|
$29,905,791
1,481,952 shares
|
— | 30 Jun 2026 |
| AMERICAN CENTURY COMPANIES INC |
13F
Company
|
2.7%
|
$23,744,313
1,176,626 shares
|
— | 30 Jun 2026 |
How to read this table
Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.
Forms 3/4/5 flow
Insider trading overview
Net insider flow leans to selling over the last 12 months. Net value: -$1,306,443.
Buys
$0
Insiders: 0
Sells
$1,306,443
Insiders: 4
Net
-$1,306,443
Shares: -52,461
Window
Last 12 months
4 rolling buckets
Buy value
Sell value
Shares: 0
Shares: 52,461
| Window (months) | Buy shares | Sell shares | Buy value | Sell value | Net value |
|---|---|---|---|---|---|
| 0-3 | 0 | 16,153 | $0 | $345,738 | -$345,738 |
| 3-6 | 0 | 0 | $0 | $0 | $0 |
| 6-9 | 0 | 18,129 | $0 | $477,141 | -$477,141 |
| 9-12 | 0 | 18,179 | $0 | $483,564 | -$483,564 |
Reporting owners
Insider holders from Forms 3/4/5
Showing 1-15 of 15 reporting-owner rows connected to Amphastar Pharmaceuticals, Inc.. Open a relationship link for the CIK-to-CIK filing trail.
Rows
15
Largest Forms 3/4/5 holder
Jack Y. Zhang
Net 12M change
-$1,306,442
Latest report
11 Aug 2026
| Name | Relationship | Holdings Value | Past Year Net Change | Change % | Valuation | Report Date |
|---|---|---|---|---|---|---|
| Jack Y. Zhang | CEO & CHIEF SCIENTIFIC OFFICER, Director, 10%+ Owner | $112,189,838 | Mixed | 15 Mar 2026 | ||
| Mary Z. Luo | COO,Chief Scientist & Chairman, Director, 10%+ Owner | $63,239,930 | Mixed | 10 Jan 2024 | ||
| Richard Koo | Director | $15,350,254 | Mixed | 07 Jun 2021 | ||
| Rong Zhou | Senior Evp, Production Center | $4,676,915 | -$256,379 | -5.2% | Mixed | 15 Mar 2026 |
| William J. Peters | CFO, EVP & TREASURER, Director | $3,885,578 | -$183,886 | -4.5% | Filing P/S | 07 Aug 2026 |
| Yakob Liawatidewi | EVP CORP ADMIN CENTER, Director | $3,294,057 | Mixed | 15 Mar 2026 | ||
| Howard Lee | Director | $3,121,666 | Mixed | 01 Jun 2026 | ||
| Floyd F. Petersen | Director | $1,850,044 | -$591,072 | -24% | Filing P/S | 11 Dec 2025 |
| David Maris | Director | $1,092,746 | Mixed | 07 Jun 2021 | ||
| Michael A. Zasloff | Director | $737,896 | Mixed | 01 Jun 2026 | ||
| Diane G. Gerst | Director | $624,901 | Mixed | 01 Jun 2026 | ||
| Richard K. Prins | Director | $601,387 | -$275,105 | -31% | Filing P/S | 11 Aug 2026 |
| Gayle Deflin | Director | $373,326 | Mixed | 01 Jun 2026 | ||
| David Russell Gaugh | Director | $283,016 | Mixed | 01 Jun 2026 | ||
| Pierce Anthony T. | Director | $159,140 | Median | 09 Jul 2026 |
Recent insider transactions for Amphastar Pharmaceuticals, Inc.
Showing up to 300 recent insider transactions from the last 12 months.
| Insider | Symbol | Class | Transaction | % | SEC-reported value | SEC-reported price | Shares | Shares owned | Date | Ownership |
|---|---|---|---|---|---|---|---|---|---|---|
| Richard K. Prins | AMPH | Common Stock | Sale | -21.2% | $161,852 | $20.30 | -7,973 | 29,625 | 11 Aug 2026 | Direct |
| William J. Peters | AMPH | Common Stock | Sale | -4.52% | $183,886 | $22.48 | -8,180 | 172,846 | 07 Aug 2026 | Direct |
| William J. Peters | AMPH | Common Stock | Options Exercise | 2.87% | 5,053 | 181,026 | 07 Aug 2026 | Direct | ||
| William J. Peters | AMPH | Employee Stock Option (right to buy) | Options Exercise | -100% | -5,053 | 0 | 07 Aug 2026 | Direct | ||
| Pierce Anthony T. | AMPH | Common Stock | Award | 7,886 | 7,886 | 09 Jul 2026 | Direct | |||
| Pierce Anthony T. | AMPH | Stock Option (right to buy) | Award | 16,646 | 16,646 | 09 Jul 2026 | Direct | |||
| Howard Lee | AMPH | Common Stock | Tax liability | -0.48% | -769 | 159,350 | 02 Jun 2026 | Direct | ||
| Richard K. Prins | AMPH | Common Stock | Award | 27.6% | 8,143 | 37,598 | 01 Jun 2026 | Direct | ||
| Richard K. Prins | AMPH | Stock Option (right to buy) | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| Howard Lee | AMPH | Common Stock | Award | 5.36% | 8,143 | 160,119 | 01 Jun 2026 | Direct | ||
| Howard Lee | AMPH | Stock Option (right to buy) | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| Michael A. Zasloff | AMPH | Common Stock | Award | 27.6% | 8,143 | 37,667 | 01 Jun 2026 | Direct | ||
| Michael A. Zasloff | AMPH | Common Stock | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| Diane G. Gerst | AMPH | Common Stock | Award | 34.3% | 8,143 | 31,899 | 01 Jun 2026 | Direct | ||
| Diane G. Gerst | AMPH | Stock Option (right to buy) | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| David Russell Gaugh | AMPH | Common Stock | Award | 129.2% | 8,143 | 14,447 | 01 Jun 2026 | Direct | ||
| David Russell Gaugh | AMPH | Stock Option (right to buy) | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| Gayle Deflin | AMPH | Common Stock | Award | 74.6% | 8,143 | 19,057 | 01 Jun 2026 | Direct | ||
| Gayle Deflin | AMPH | Stock Option (right to buy) | Award | 17,365 | 17,365 | 01 Jun 2026 | Direct | |||
| Yakob Liawatidewi | AMPH | Common Stock | Tax liability | -0.84% | -1,033 | 121,892 | 15 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Common Stock | Tax liability | -0.71% | -1,225 | 171,554 | 15 Mar 2026 | Direct | ||
| William J. Peters | AMPH | Common Stock | Tax liability | -1.11% | -1,973 | 175,063 | 15 Mar 2026 | Direct | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.23% | -2,908 | 1,245,125 | 15 Mar 2026 | See footnote | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.33% | -9,784 | 2,990,052 | 15 Mar 2026 | Direct | ||
| William J. Peters | AMPH | Common Stock | Tax liability | -1.83% | -3,297 | 177,036 | 10 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Common Stock | Tax liability | -1.27% | -2,215 | 172,779 | 10 Mar 2026 | Direct | ||
| Yakob Liawatidewi | AMPH | Common Stock | Tax liability | -1.5% | -1,870 | 122,925 | 10 Mar 2026 | Direct | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.35% | -4,395 | 1,248,033 | 10 Mar 2026 | See footnote | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.49% | -14,785 | 2,999,836 | 10 Mar 2026 | Direct | ||
| William J. Peters | AMPH | Common Stock | Award | 48.2% | 58,693 | 180,333 | 09 Mar 2026 | Direct | ||
| William J. Peters | AMPH | Employee Stock Option (right to buy) | Award | 121,071 | 121,071 | 09 Mar 2026 | Direct | |||
| Rong Zhou | AMPH | Common Srock | Award | 29.1% | 39,432 | 174,994 | 09 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Employee Stock Option (right to buy) | Award | 81,341 | 81,341 | 09 Mar 2026 | Direct | |||
| Yakob Liawatidewi | AMPH | Common Stock | Award | 39.7% | 35,450 | 124,795 | 09 Mar 2026 | Direct | ||
| Yakob Liawatidewi | AMPH | Employee Stock Option (right to buy) | Award | 73,126 | 73,126 | 09 Mar 2026 | Direct | |||
| Jack Y. Zhang | AMPH | Common Stock | Award | 6.14% | 72,462 | 1,252,428 | 09 Mar 2026 | See footnote | ||
| Jack Y. Zhang | AMPH | Common Stock | Award | 6.37% | 180,504 | 3,014,621 | 09 Mar 2026 | Direct | ||
| Jack Y. Zhang | AMPH | Employee Stock Option (right to buy) | Award | 149,472 | 149,472 | 09 Mar 2026 | See footnote | |||
| Jack Y. Zhang | AMPH | Employee Stock Option (right to buy) | Award | 372,338 | 372,338 | 09 Mar 2026 | Direct | |||
| William J. Peters | AMPH | Common Stock | Tax liability | -1.73% | -2,146 | 121,640 | 06 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Common Stock | Tax liability | -0.99% | -1,357 | 135,562 | 06 Mar 2026 | Direct | ||
| Yakob Liawatidewi | AMPH | Common Stock | Tax liability | -1.26% | -1,144 | 89,345 | 06 Mar 2026 | Direct | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.26% | -3,077 | 1,179,966 | 06 Mar 2026 | See footnote | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.27% | -7,773 | 2,834,117 | 06 Mar 2026 | Direct | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.21% | -2,432 | 1,183,043 | 04 Mar 2026 | See footnote | ||
| Jack Y. Zhang | AMPH | Common Stock | Tax liability | -0.2% | -5,769 | 2,841,890 | 04 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Common Stock | Tax liability | -0.81% | -1,124 | 136,919 | 04 Mar 2026 | Direct | ||
| Yakob Liawatidewi | AMPH | Common Stock | Tax liability | -1.06% | -965 | 90,489 | 04 Mar 2026 | Direct | ||
| William J. Peters | AMPH | Common Stock | Tax liability | -1.39% | -1,744 | 123,786 | 04 Mar 2026 | Direct | ||
| Rong Zhou | AMPH | Common Stock | Sale | -6.62% | $256,379 | $26.20 | -9,787 | 138,043 | 17 Dec 2025 | Direct |
* marks a reported price that did not pass the local price check.