A high-performance solar-blind phototransistor, which is based on hydrogen-terminated diamond was fabricated and reported. The fabricated phototransistor was based on metal–semiconductor field effect transistor architecture with a high photoresponsivity (2.48 × 104 A/W), high external quantum efficiency (1.44 × 105), and high detectivity (5.08 × 109 Jones) under 213-nm light illumination (437 W/m2). At 5240 W/m2 light illumination, the change in drain current exceeds six orders of magnitude. Through transient response measurement, the rise/decay time of the phototransistor is about 88 / 36 ms and there is no significant persistent photoconductive effect.