A variety of lasers have been applied to trimming thin and thick film resistors in the last ten years, ranging from pulsed argon lasers for thin film cermet resistors to CO2 lasers for thick film resistors. At present, the Q-switched YAG laser dominates the resistor trimming technology because of its high repetition rate (5-10 KHz) and its relatively high pulse power (2-20 Kwatts). The xenon laser, on the other hand, with its 300 watts pulse power and 200 Hz repetition rate, is taking over the thin film semi-automatic resistor trimming technology. At an output of 535 nm, the wavelength of the xenon laser is half of the 1060 nm of the YAG laser and thus provides a diffraction limited spot size which is one half as large. With a one inch focal length objective lens the YAG laser offers a spot size of .0005 inch where a xenon laser provides a .00025 inch spot size. As thin film resistor geometries approach a .0005 inch width, it is becoming evident that a spot size of .00025 or less is essential. Certain substrates such as circuit boards are not damaged (scarred) by the xenon wavelength as readily as with the YAG. Thin film resistors on substrates of glass, ceramic and circuit board have been trimmed in a variety of geometries with the xenon laser. As the xenon laser does not require special power or water facilities, it forms the basis for a cost effective resistor trimming system in thin film resistor production.