An electronic device is provided. The electronic device includes a display having a first surface, a metal frame structure configured to form a side surface of the electronic device, a rear plate having a second surface facing a third direction, at least one antenna module disposed inside the side surface and having a radiation surface, at least one dielectric layer having at least a partial region attached to the radiation surface, and a wireless communication circuit configured to transmit or receive an radio frequency (RF) signal to or from the at least one antenna module, in which the at least one dielectric layer includes a first dielectric sheet and a second dielectric sheet, in which the first dielectric sheet is made of a thermal conductive material having a first permittivity and the second dielectric sheet is made of a material having a second permittivity larger than the first permittivity.