An electro-optically (EO) $Q$Q-switched Tm:YAP laser with high peak power was demonstrated based on a ${{\rm La}_3}{{\rm Ga}_5}{{\rm SiO}_{14}}$La3Ga5SiO14 (LGS) crystal. The EO modulator was operated in a pulse-on mode driven by a 1/4 wave voltage of 2400 V, which was the lowest voltage designed for LGS-based EO modulators at 2 µm, to the best of our knowledge. At a repetition rate of 200 Hz, a maximum single-pulse energy of 3.15 mJ was obtained with a minimum pulse duration of 17 ns, corresponding to a peak power as high as 185.3 kW.