This book discusses the role of semiconductor technology in kinase drug discovery applications. It explores the design of electronic and optical techniques to understand the phosphorylation of proteins. There are two major electronic characteristics of phosphorylation that aid in its detection and subsequently biosensor development: first is the release of a proton upon phosphorylation of a protein (change in pH) and second is the addition of negative charge to the protein upon its phosphorylation. In particular, this book reports an electrolyte–insulator–semiconductor sensing structures to detect the pH changes associated with phosphorylation and metal–insulator–semiconductor structures to detect the charge change upon phosphorylation of proteins. Major application of these devices is to screen inhibitors of kinases that mediate phosphorylation of proteins. Inhibitors of kinase act as drugs to prevent or cure diseases due to the phosphorylation of proteins. With the advancements in VLSI and microfluidics technology these techniques can be extended into arrays for high throughput screening of novel drugs.