Dopamine (DA) is an important neurotransmitter that is involved in neuronal signal transduction and several critical illnesses. However, the concentration of DA is extremely low in patients and is difficult to detect using existing electrochemical biosensors with detection limits typically around nanomolar levels (∼10(-9) M). Here, we developed a nanoelectronic device as a biosensor for ultrasensitive and selective DA detection by modifying DNA-aptamers on a multiple-parallel-connected (MPC) silicon nanowire field-effect transistor (referred to as MPC aptamer/SiNW-FET). Compared with conventional electrochemical methods, the MPC aptamer/SiNW-FET has been demonstrated to improve the limit of DA detection to <10(-11) M and to possess a detection specificity that is able to distinguish DA from other chemical analogues, such as ascorbic acid, catechol, phenethylamine, tyrosine, epinephrine, and norepinephrine. This MPC aptamer/SiNW-FET was also applied to monitor DA release under hypoxic stimulation from living PC12 cells. The real-time recording of the exocytotic DA induced by hypoxia reveals that the increase in intracellular Ca(2+) that is required to trigger DA secretion is dominated by an extracellular Ca(2+) influx, rather than the release of intracellular Ca(2+) stores.