An infrared optical field effect transistor has been developed using a thin film of Lead Titanate (PbTiO.sub.3) deposited on a n/p.sup.+ Si substrate by RF magnetron sputtering. This transistor possesses excellent pyroelectric properties and can, therefore, be operated even at room temperature. The infrared optical field effect transistor has the following features associated with rapid bulk channel structure and higher mobility: 1. Can be operated at room temperature, unlike quantum type IR sensors which can only operate at very low temperature (-100.degree. C..about.-200.degree. C.), which results in higher costs. 2. High speed response with only 2.3 .mu.s of rise time. This is much faster than other types of thermal infrared optical field effect transistors. 3. Easy to fabricate an integrated sensor device.