The performance of Pd/GaN Schottky diodes fabricated on a-plane GaN for hydrogen sensing was investigated. Pd Schottky diode on non-polar a-plane (11-20) GaN layers shows large increases in both forward and reverse bias current upon exposure to 4% H2 in N2. The barrier height reduction due to hydrogen exposure is 0.11 eV with long recovery times (>25 mins) at room temperature. The sensitivity to hydrogen is significantly greater than for diodes on conventional c-plane (Ga-polar) GaN.