Abstract: The dynamic performance of a dual-emitter phototransistor (DEPT) was studied. In the static case of a DEPT under a 12.5 muW optical power, the emitter-induced gain effect from photocurrent modulation improves collector photocurrent (88 to 129 muA). For the DEPT as an electro-optical switch with a 2 V supply voltage, the stable electrical logic swing is 0.41 V for a 1 V clock signal. When a short-period clock signal is applied, a clear electrical logic swing larger than 1.2 V is achieved. The emitter-induced gain effect from both photocurrent modulation and junction-voltage modulation is also introduced to clearly describe DEPT dynamic performance.