This letter presents a fully monolithic microwave-integrated circuit (MMIC) substrate integrated waveguide (SIW) filter using integrated passive device (IPD) technology for Q-band applications. It is challenging to implement an SIW bandpass filter (BPF) at the chip level due to the complex process rules of chip processing. A possible solution is to use multiple TE101 mode SIW resonators to build a BPF via magnetic coupling. However, this layout method can easily cause a larger chip aspect ratio, which is not conducive to the chip’s reliability. To this end, the proposed SIW filter adopts four SIW resonators to form a highly selective BPF through planar stacking. Measurement results show that the minimum insertion loss of the proposed SIW filter is 3.07dB, and fractional BW (FBW) of 4.4% with a compact size of 0.199λ₀², including pad, which is among the best compared to previously reported SIW chip BPFs.