This paper proposes a novel high-gain millimeter-wave microstrip array antenna formed on a multi-layer low temperature co-fired ceramic (LTCC) substrate. The proposed antenna employs a microstrip antenna with stacked rings. This paper describes the design and characteristics of the proposed antenna. The antenna performance is also calculated by using electro-magnetic simulation. The thickness of the proposed antenna is 0.5 mm and the proposed antenna achieves the antenna gain of 13.3 dBi in calculation at a 60-GHz band. Moreover, we confirmed a good agreement of an calculated results and the measured results in the radiation pattern and achieved the absolute gain of 9.4 dBi with the measuring loss of the RF probe that is about 1.1 dB at 56 GHz. It is clear that the proposed antenna is suited for compact and low-profile millimeter-wave system-on-package.