A compact and low-insertion-loss amplitude-shifted keying (ASK) modulator suitable for operations in D-band (110 GHz 170 GHz) has been designed and successfully integrated with a 65-nm CMOS technology. The structure of the modulator is a transmission-line type single-pole-single-throw (SPST) switch. To minimize the insertion loss, a single section of a transmission line is used with two shunt transistors. The modulator exhibits an insertion loss of lower than 3.6 dB, measured without de-embedding, and an isolation of higher than 19.5 dB in the D band. The transient behavior of the modulator has been characterized by using a pulse generator, revealing an operation suitable for over-1Gbps applications.