Process capability indices have been introduced to provide numerical measures on whether a manufacturing process is capable of reproducing items meeting the specifications predetermined by the product designers or the consumers. Process yield is one of the most common criteria used in the manufacturing industry for measuring process performance. The formula Spk has been proposed to calculate the process yield for normal processes. The formula Spk provides an exact measure on the process yield. Unfortunately, the statistical properties of the estimated Ŝpk are mathematically intractable. In this paper, we apply the bootstrap simulation method to construct the lower confidence bound of Spk. We then present a real-world application to the liquid-crystal display module process, to illustrate how we may apply the formula Spk to actual data collected from the factories.