Amphastar Pharmaceuticals, Inc.
Ownership
Ownership Structure
Who owns Amphastar Pharmaceuticals, Inc. (AMPH)? This page shows the largest institutions and funds, the ownership structure and the latest insider transactions. 73.6% of the shares are freely tradable; institutional investors hold 76.5%.
Largest Shareholders
Institutions
| Name | Stake (%) | Shares | Change (%) | Date |
|---|---|---|---|---|
| BlackRock Inc | 12.74 | 5,421,343 | -0.7 | 03/31/2026 |
| Dimensional Fund Advisors, Inc. | 5.42 | 2,305,107 | +13.7 | 06/30/2026 |
| State Street Corp | 3.78 | 1,607,515 | +4.9 | 03/31/2026 |
| Vanguard Capital Management, LLC | 3.63 | 1,543,655 | +0.0 | 03/31/2026 |
| Fuller & Thaler Asset Management Inc | 3.28 | 1,395,139 | -50.0 | 03/31/2026 |
| American Century Companies Inc | 2.77 | 1,176,626 | +15.6 | 06/30/2026 |
| Marshall Wace Asset Management Ltd | 2.41 | 1,025,640 | -17.1 | 03/31/2026 |
Funds
| Name | Stake (%) | Shares | Change (%) | Date |
|---|---|---|---|---|
| iShares Core S&P Small-Cap ETF | 4.86 | 2,065,760 | +0.0 | 08/31/2026 |
| Avantis US Small Cap Value ETF | 2.68 | 1,141,881 | +0.2 | 08/31/2026 |
| Vanguard MStar Total Stk Mkt Idx Invest | 2.48 | 1,055,676 | +0.0 | 07/31/2026 |
Largest reported positions according to regulatory filings; stake as a percentage of shares outstanding, change versus the previous filing. Source: fundamentals data.
Insider holdings
| Person | Role | Shares | Value | As of | Type |
|---|---|---|---|---|---|
| Peters William J | CFO, EVP & TREASURER | 172,846 | 4,079,166 $ | Aug 7, 2026 | direct |
| Zhou Rong | SENIOR EVP, PRODUCTION CENTER | 169,203 | 3,993,191 $ | Sep 16, 2026 | direct |
| Prins Richard K | Director | 29,625 | 699,150 $ | Aug 11, 2026 | direct |
| Pierce Anthony T | Director | 7,886 | 186,110 $ | Jul 9, 2026 | direct |
Holdings as of each person's most recent SEC Form 4 filing — excluding options and RSUs, which are not shares yet. Holdings may have changed between two filings.
Insiders
Insider Transactions
| Date | Person | Role | Type | Shares | Price | Value |
|---|---|---|---|---|---|---|
| Sep 16, 2026 | Zhou Rong | SENIOR EVP, PRODUCTION CENTER | Sell | 10,000 | 23.94 | 239,404 |
| Sep 16, 2026 | Zhou Rong | SENIOR EVP, PRODUCTION CENTER | Other | 10,000 | 13.35 | 133,500 |
| Sep 2, 2026 | Zhou Rong | SENIOR EVP, PRODUCTION CENTER | Sell | 3,187 | 23.63 | 75,306 |
| Aug 11, 2026 | Prins Richard K | Director | Sell | 7,973 | 20.30 | 161,852 |
| Aug 7, 2026 | Peters William J | CFO, EVP & TREASURER | Sell | 8,180 | 22.48 | 183,886 |
| Aug 7, 2026 | Peters William J | CFO, EVP & TREASURER | Other | 5,053 | 19.79 | 99,999 |
| Jul 9, 2026 | Pierce Anthony T | Director | Other | 7,886 | 0.00 | – |
Reportable transactions by officers and major shareholders from SEC Form 4 filings. "Other" includes things like stock grants and option exercises without a buy/sell character. View all insider transactions →
Data as of: September 18, 2026 · Source: fundamental data & SEC filings (annual and quarterly reports, 10-K/10-Q)
Note: pure fact-based analysis, not investment advice and not a solicitation to buy or sell. All figures without guarantee.