This paper reveals a durable trimming condition of thin film resistors as a part of snubber circuits in high power electronic modules including IGBT converters. Our previous study clarified that the maximum voltage to apply to the resistors is limited by thermal destruction of the resistors due to the pulsed power injection. With careful failure analysis and surface observations, this paper provides an additional insight that dimensions of the indispensable trimming patterns affect the thermal destruction. Electro-thermal analysis results show that the optimized dimensions of the trimmed shapes can suppress temperature rise of the most critical area up to one sixth compared to the most pessimistic shape.