In this paper, we investigate the applicability of parallel sequence spread spectrum (PSSS) modulation in high bandwidth millimeter wave communication systems using a 240GHz monolithic microwave integrated circuit (MMIC) based radio frequency (RF) frontend. The transmitter (Tx) and receiver (Rx) are connected directly via an attenuator in an incoherent back-to-back setup using two independent local oscillator (LO) sources. Although the system was restricted to phase modulated signals due to limited linearity when using conventional modulated signals, a transmission using a multivalent PSSS sequence with a spectral efficiency of 1 bit/s/Hz succeeded thanks to the introduced coding gain. The recovered data is evaluated in terms of eye opening and bit error rate (BER). At a gross data rate of 20 Gbit/s, an eye opening of 40% and a BER of 5.4 × 10-5 were observed.