Abstract Ultra‐broadband photodetectors based on semimetal crystals have recently become popular because of their gapless band structures. In particular, semimetal crystals have large carrier mobility or high Seebeck coefficient; this almost eliminates the possibility of using semimetal crystals as photodetectors. In addition, a larger temperature gradient can cause photocurrent generation based on the photothermoelectric effect. Surprisingly, the TaTe 2 crystal has a huge absorption coefficient (≈10 4 cm −1 ), a minimal specific heat (≈0.172 J g −1 K −1 ), and a low thermal conductivity (0.3 W m −1 K −1 ), which is beneficial for generating a high photothermal conversion efficiency of 30.2%, despite its small Seebeck coefficient, and achieving a large temperature gradient occurs for the heat generated by external illumination. Herein, the possibility of photoresponse based on the TaTe 2 detector is explored, which has a low carrier mobility (≈10 cm 2 V −1 s −1 ) and a small Seebeck coefficient (≈7.1 µV K −1 ). The self‐powered TaTe 2 photodetector can also provide a competitive photoresponse range from 355 to 2715 nm and exhibit a maximum responsivity of 1.1 mA W −1 with a detectivity of 4.7 × 10 8 Jones at 455 nm. This study provides a new design scheme and operating mechanism for semimetal photodetectors and enriches semimetal crystal photodetectors.