A full-wave numerical approach, based on the two-dimensional finite difference time domain (FDTD) method, is developed for the accurate analysis of channel multilayer and multiple quantum well (MQW) waveguides. Numerical results in terms of field distributions and dispersion characteristics are given and compared with available results obtained with vector finite element method. The scalar approximation technique, based on the 2-D FDTD method, is also investigated and it's limitations of the validity and accuracy are pointed out.