This work shows the results of silicon MOS device as a sensor of chemical image, for the detection and classification of hydrogen and ammonia gases, through the Scanning Light Pulse Technique (SLPT). The gate of the device was built from an Au-Pd bimetallic electrode, with nanometric thickness. It was proposed an X Y automatic position system for scanning the light pulsed beam, based on the PID control and on the Labview® software. The data acquisition process was also automated via virtual instrumentation defined by the Labview® software. The MOS device showed maximum sensitivity for hydrogen and ammonia gases when the width of the depletion layer has maximum value. The chemical images obtained from the MOS sensor response, in SLPT operation mode for hydrogen and ammonia environments, respectively, showed characteristic patterns to each kind of gas, independent of the concentration used, allowing the complete classification of these gases. The results obtained in the present work suggest the possibility of implementing an electronic nose system, using only one sensor.