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The technology of thin film transistor liquid crystal display (LCD) has become more popular due to great demand for worldwide consumer electronic products. Driver integrated circuit (IC) is a critical device that is embedded sophisticated circuits to drive panels. Since narrow border design on display products is current trend, dimensions of driver ICs are shrunken. In the high-density LCD driver ICs, the operation of wafer sawing is essential and needs accurate yield assessment. However, inevitable process variance changes could arise from sawing machine, material, operation, and workmanship, and may not be detected within short time. Conventionally, manufacturing yield is evaluated applying typical yield measure index method under the assumptions that the processes are stable and normal. To assess manufacturing yield for Gamma wafer sawing processes more accurately, we present a modified yield measure index method. Using the proposed method, the magnitudes of the undetected variance change, which are functions of the detection power of the S2 chart, are incorporated into the evaluation of manufacturing yield. In addition, we demonstrate, mathematically, that the accommodation would not be affected by the scale parameter of Gamma distribution. For illustration purpose, a real-world case in a wafer sawing factory which is located on the Science-based Industrial Park in Hsinchu, Taiwan, is presented.