There is considerable interest in wideband pulse modulation at mm-Wave frequencies for application in radar and medical imaging systems [1,2]. Accuracy and resolution in these respective systems are determined by the minimum pulse width (PW). PWs down to 300ps have previously been reported for 24/79GHz carrier frequencies [1,3]. This paper presents the design of the first pulse-based transmitter with integrated antenna to achieve sub-100ps PWs at mm-Wave frequencies in silicon. The transmitter generates variable measured PWs in the range of 35 to 376ps. To obtain this performance, hybrid PA/antenna switching has been explored in combination with high-speed digital switching circuitry.