The present invention is to provide a group III nitride tunneling junction structure with a low tunneling potential barrier, in which Si layer or a group III-V compound semiconductor In(a)Ga(b)Al(c)As(d)[N]P(e) (0.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.1, 0.ltoreq.c.ltoreq.1, 0.ltoreq.d.ltoreq.1, 0.ltoreq.e.ltoreq.1) which has a smaller band gap than that of Al(x)Ga(y)In(z)N (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1) and can be doped with a high concentration of p is inserted into a tunneling junction based on a P.sup.++-Al(x)Ga(y)In(z)N (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1) layer and a N.sup.++-Al(x)Ga(y)In(z)N (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1) layer. This tunneling junction structure will be useful for the fabrication of a highly reliable ultrahigh-speed optoelectronic device.