Electro-optic sampling technique is employed to reveal the generation of teraher tz (THz) radiation via optical rectification from reactive ion etched ZnTe surfa ces. The pulsewidth of the observed THz radiation is ～0.25ps. The electro-optic coefficient of the ZnTe samples is found to decrease with the increase of the r adio frequency (RF) power. By calculating the frequency response function, we di scuss the THz bandwidth under different values of RF plasma power.