A high voltage semiconductor device includes a semiconductor substrate, a first region, a second region, and an interconnection region. The first region includes an N-type first semiconductor region, an N-type drain region formed in the N-type first semiconductor region, a P-type first body region, an N-type source region formed in the P-type first body region, and a gate electrode formed between the N-type source region and the N-type drain region. The second region includes an N-type second semiconductor region, and a P-type second body region formed in the N-type second semiconductor region. The interconnection region is disposed between the first region and the second region, and includes a first insulation layer formed between the N-type first semiconductor region and the N-type second semiconductor region, a metal interconnection formed on the first insulation layer, and an isolation region formed in the substrate and disposed below the first insulation layer.