An antenna device includes a radio frequency (RF) die, a first dielectric layer, a feeding line, a ground line, a second dielectric layer, and a radiating element. The first dielectric layer is over the RF die. The feeding line is in the first dielectric layer and is connected to the RF die. The ground line is in the first dielectric layer and is spaced apart from the feeding line. The second dielectric layer covers the first dielectric layer. The radiating element is over the second dielectric layer and is not in physically contact with the feeding line.