This paper presents two high-Q circular resonators utilizing low temperature co-fired ceramic (LTCC) multilayer circuits for millimeter-wave system-on-package applications. A resonator including zigzagged dual-row via posts for tightly confining electromagnetic energy as a metallic boundary wall will be presented. Another resonator containing the zigzagged dual-row via posts and a lambda/4 short stub on a feeding via post in the circular resonator is used for transmitting energy in the resonator to output load without losses. Simple theories for obtaining high-Q factors using zigzagged dual-row via posts and the feeding technique with the lambda /4 short stub are derived. A total of four layers are used to construct the resonator with a height of 300 mu m (three layers); an additional layer is used for the probe excitation and signal feeding line. The signal feeding line is employed to connect a negative resistance generator monolithic microwave integrated circuit ((-)R MMIC) that consists of conductor backed coplanar waveguide (CBCPW), which is implemented on a layer. A CPW-type double bond wire connects the resonator and (-)R MMIC. The measurement results show that the first and second resonant modes are TM010 at 29.75 GHz and TE010 at 46.75 GHz, respectively. Although the unloaded Q value of the conventional resonator is 204, the proposed resonator with zigzagged dual-row via posts achieved an unloaded Q value of 249, which is a 22.1% improvement. Further, the new resonator with the lambda/4 short stub and zigzagged dual-row via posts yielded an unloaded Q of 296, an improvement of 45.1% for the first resonant mode. In order to verify the resonator performances, the oscillator integrating the proposed resonator is evaluated. The measured output power and phase noise of the oscillator is 18.8 dBm at 27 GHz and -104.67 dBc/Hz at 1 MHz offset, respectively. It can be implemented easily without requiring additi- - onal processes or any degradation of performance and therefore is suitable to implement in high integrated systems for millimeter-wave applications.