Field plate structures for gallium nitride (GaN) high voltage transistors are disclosed. In one aspect, a transistor includes a GaN substrate, a source region formed on the GaN substrate, a drain region formed on the GaN substrate and separate from the source region, a gate region formed between the source region and the drain region, a pedestal formed on the GaN substrate and positioned between the gate region and the drain region, and a field plate electrically coupled to the source region, where the field plate extends from a proximal region positioned between the source region and the pedestal, towards the drain region, where at least a portion of the field plate overlaps at least a portion of the pedestal.