The characteristics of plasma waves in gated two-dimensional electron gas systems are discussed. We numerically discuss the effect of the intrinsic nonlinearity of plasma waves on their propagation. Moderate nonlinearity results in the development of solitons, as suggested by [Govorov etal, JETP Lett. 70, 488 (1999)]. In addition, backward-traveling pulses develop when the degree of nonlinearity becomes large.