In this paper, we present GaN-on-Si vertical transistors consisting of a 6.7 pm thick n-p-n heterostructure grown on 6-inch silicon substrates by MOCVD. The fabricated vertical trench gate MOSFETs exhibited E-mode operation with a threshold voltage of 3.3 V and an on/off ratio of over 108. A specific on-resistance of 6.8 mSL"cm2 and a high off-state breakdown voltage of 645 V were achieved. These results show the great potential of the GaN-on-Si platform for the next generation of cost-effective power electronics.