Flowerlike ZnO nanorods were synthesized by the hydrothermal process. A simple two-step process was developed for growing ZnO nanorods on the silicon substrates at about 85 degrees C. The concentration of zinc acetate dehydrate pretreatment is 0.01M. The x-ray diffractometer pattern of ZnO nanorods at 2 theta=31.77 degrees, 34.42 degrees, and 36.25 degrees indicates three reflection peaks of hexagonal wurtzite structure, (100), (002), and (101), respectively. It has been shown that the ZnO nanorods are of single hexagonal phase of wurtzite structure. The scanning electron microscopy image revealed that the average diameter of ZnO nanorods was about 360 nm. In addition, the ZnO nanorods/Si structure was utilized as a pH sensor head and connected with the metal-oxide-semiconductor field-effect transistor when the extended-gate field-effect transistor was finished. Afterward, the semiconductor parameter analysis instrument (Keithley 4200) was used to measure the current-voltage characteristic curves in the different pH buffer solutions. The experimental result found that the pH sensing response is obtained and the output voltage shifted right with increasing pH values.