This paper proposes a highly efficient multilayer parasitic microstrip antenna array that is constructed on a multilayer Teflon substrate for millimeter-wave system-on-package modules. The proposed antenna achieves a radiation efficiency of greater than 91% and an associated antenna gain of 11.1 dBi at 60 GHz. The antenna size is only 10 mm /spl times/ 10 mm. Additionally, this paper describes a 60-GHz-band prototype antenna employing a multilayer Teflon substrate that is well suited to achieving high gain and a wide bandwidth. The measured performance of the prototype antenna is also presented.