Several heterostructure samples of varying complexity were studied by spectroscopic ellipsometry. The analysis of this data, requiring computer modeling for optimum correlation between model and experiment, demonstrates the ability of this technique to apply multiparameter analysis to complex samples. Our results provide an absolute measure of up to seven material parameters, with 90% confidence limits in the range 0.1-2% for at least the four most sensitive parameters. Such accuracies are improved by a factor of 5-10 over previous reports for such complex samples. Furthermore, the method is demonstrated to provide sensitive detection of interfaces, even when buried under ≥0.5 μm of GaAs.