This book is the result of the research activities carried out at the Polytechnic School of the University of São Paulo to obtain an MSc. degree in Electrical Engineering. The objective of the work was to verify the ability of Gate-Controlled Diodes to respond selectively to the light's wavelength, being able then to work as color sensors. The key idea is to drive such devices into deep depletion operation conditions in order to increase its depletion region beyond its maximum width. Computer simulations were used to characterize the device's electrical behavior and also to investigate the absorption of light with different wavelengths at a PN junction. Also, some electrical characterization of test-structures was carried out in order to verify the fabrication processes used to manufacture Gate-Controlled Diodes.