Structural and electronic properties of Al0.3Ga0.7As/GaAs heterojunction and GaAs pn junction systems are investigated by cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S). The cross-sectional samples were prepared by passivating ex situ with a sulfide [(NH4)2S] solution and were transferred into an ultra-high vacuum system for STM/S studies. It is found that passivated samples are advantageous for the measurements of scanning tunneling spectroscopy. The STM/S results and the experimental details are reported.