I am unable to find any references to any semi auto striker fired pistol before the Borchardt C93. It may be that the C93 was the first striker fired pistol.
And while the C93 might be considered the first mass produced semi auto (different folks have different numbers for what constitutes "mass production", one I standard I have heard is 5,000 units.) The C93 was not common, I think only a few thousand were made, but that could be enough I suppose.
The appellation of "first successful (or commercially successful) semi auto is usually given to the Mauser C96 aka Broomhandle, which is not a striker fired pistol. The C93 might be the first mass produced, but the Mauser 96 was a commercial success (for a time, anyway), and many, many, many more were made than Borchardts.