The physical characteristics of high resistivity CdTe which are relevant to its use for electro‐optic modulation have been investigated at 3.39 and 10.6 &mgr;. The unclamped electro‐optic characteristicn0 3r41of CdTe was found to be 12 × 10−11m/V and the absorption coefficient is 0.006 cm−1. Our measurements indicate that CdTe will be a very important material for electro‐optic modulation in the infrared.