Nondestructive characterization of semiconductor surfaces and interfaces by the surface acoustic wave (SAW) technique is demonstrated and reviewed. In the past few years, the sensitivity and applicability of this method has been greatly enhanced by the introduction of a new delay line structure and the use of two beam spectroscopy. The monitored signal in the following experiments is the transverse acoustoelectric voltage (TAV). Two beam spectroscopy (both beams are monochromatic) is applied to GaAs, InP and CdS in order to reveal the subband gap energy level structures. The presented data on the subband gap interface states which are due to the intrinsic nature of the surface discontinuity or due to the interface with other materials (electrolyte, oxide, etc.) includes the following: 1) High resistivity GaAs surface states, the GaAs/oxide interface states and the effect of wet anodic oxidation in increasing the density of these states, 2) Exciton absorption and energy levels in GaAs, InP at low temperature and the observation of quenching effect on the absorption peak which is more pronounced in GaAs due to the higher interface states density, 3) Interface states at CdS/electrolyte junction which are enhanced by the photo anodization of CdS, working under short circuit current in a semiconductor liquid junction solar cell configuration. The new delay line structure enabled us to vary the surface potential via a small external DC field (comparable to C-V technique) while monitoring the TAV amplitude and transient time constants. Thus parameters such as generation lifetime, oxide charge, flat band voltage and surface generation velocity are experimentally determined for silicon wafers. Nondestructive depth profiling of the free carrier concentration and some of the above parameters are also demonstrated. Zero bias surface condition and the recombination center energy level within the silicon bandgap are determined. This technique is being presently applied to (HgCd)Te samples.