Dear zhancang, I am using LTSpice and looks like the model works like this:
*$
* PINSEQ: 1 =Drain
* | 2 =Gate
* | | 3 =Source
* | | |
.SUBCKT GaNHEMT 20 10 30
LGATE 10 11 0.47N
RGATE 11 12 2.3
CG 10 30 4.6P
CRSS 12 13 0.688P
CISS 12 14 13.81P
LS 14 30 0.0060N
CS 14 30 5.25P
LD 13 20 0.661N
CD 20 30 5.1P
J1 17 12 14 GF1 ; D G S PSPICE GASFET Model
J2 13 14 17 GF2 ; D G S PSPICE GASFET Model
RGF 13 17 10000
.MODEL GF1 NJF LEVEL=1
+BETA=1.6 RS=0.56 RD=0.02 VTO=-3.8 ALPHA=1
.MODEL GF2 NJF LEVEL=1
+BETA=25 RS=0.11 RD=0.08 VTO=-3.7 ALPHA=1
.ENDS GaNHEMT
*$
Let me know if this works for you.