In this paper, static and dynamic thermo-optical numerical analysis of a Digital Optical Switch (DOS), based on amorphous silicon waveguide and operating at the infrared communications wavelength of 1550 nm, are presented. The aim of our design is to achieve good performances in terms of cross talk and switching time, considering relaxed requirements for the realization of device: large cross section single mode waveguides and an angle between the output branches not too small. Using a low temperature difference between the two output branches, an optical switching with a crosstalk of 25 dB and a response time of the order of ten microseconds are obtained. The device, designed for low-cost photonic applications, could be easily integrated in silicon optoelectronic circuits.