A Ga0.8In0.2As/GaAs thermally actuated optical switch has been demonstrated for unpolarized 1.08 &mgr;m light. Its measuredon:offcontrast ratio of 4.7 was produced electrically by changing the applied voltage from 0 to 3.2 V on a device with a 2.25‐&mgr;m‐thick Ga0.8In0.2As active layer. The ‘‘on’’ insertion loss was 3.8 dB. Theon:offchange in Ga0.8In0.2As absorption coefficient was 6660 cm−1. The switching current density was 9.7 A/cm2. The thermal switching energy can be supplied optically for an all‐optical switch.