In this letter, we introduce and demonstrate the concept of slanted tri-gates to enhance the breakdown voltage (V-BR) in lateral GaN power devices. Conventionally, field plates (FPs) are used to enhance the V-BR by distributing more homogeneously the electric field near the gate electrode, which is mainly determined by their pinch-off voltage (V-p). These FPs however rely on a vertical approach, in which V-p is usually designed via the thickness of the FP oxide. On the other hand, the slanted tri-gate relies on a lateral design to tailor its V-p, by simply changing the width (w) of their nanowires lithographically. Here, we demonstrate this concept for AlGaN/GaN-on-silicon MOSHEMTs resulting in an increase of similar to 500 V in V-BR compared with the counterpart planar devices. These devices presented a high V-BR of 1350 V with a small gate-to-drain separation (L-GD) of 10 mu m, along with a record high-power figure-of-merit of 1.2 GW/cm(2) among GaN-on-silicon lateral transistors.