Lead is one among the most hazardous heavy metals. Heavy metal cannot be metabolized or digested by human body, therefore, heavy metal accumulates in our body through time. Lead in human body damages the nervous system, impairs vision, hearing and even cause joint and muscle pain. Mostly lead ions get in to human body by ingestion, so detecting lead ion in drinking water, tap water and liquid form of food is very important. However, traditional laboratory detection methods of lead ion are complex and time consuming and requires heavy and expensive machinery. Though the electrochemical ion selective electrode is easy to use, its poor stability and larger detection limit are huge disadvantages. In this research, we devised a small size, highly sensitive, low detection limit, short response time and easy to fabricate lead ion selective high electron mobility transistors (ISHEMT). This device is easy to use and can measure the lead concentration in water quickly with the combination of ion-selective membrane and AlGaN/GaN HEMT. The sensing mechanism depends on electrical double layer (EDL) gating coupled with high electric field to enhance the sensitivity of ISHEMT beyond the limit of ideal Nernst sensitivity. World Health Orgnization (WHO) suggests that lead ion in drinking water should be lower than 10ppb, equal to 4.8310^-8 M. This device can detect lead ion concentration form 10^-5 M to 10^-10 M, covering the wide dynamic range according to WHO’s suggestion and even higher sensitivity can be achieved by optimizing sensor design. Such high sensitivity and low detection limits are highly desirable for consumers who intend to regularly monitor the water quality, for food and environmental safety. In contrast, testing lead ion in water by ICP-MS takes several hours and the instrument occupies larger space. With this lead ISHEMT, we can determine the lead concentration in water in 10 minutes and even get better sensitivity and lower detection limit, in comparison with conventional laboratory based techniques. Not only lead, but also other heavy metals, for example mercury and cadmium, can use similar methodology to get better sensitivity and detection limit. This design makes quality monitoring of water we consume in daily life become much easier and convenient.