We demonstrate a flat transconductance (gm) while maintaining relatively high gm (~170mS/mm for extrinsic ~ 320mS/mm for intrinsic) and current (~ 1A/mm) with a new graded AlGaN/GaN high electron mobility transistor (HEMT) structure (tcap = 11nm). The graded structure is constructed with an abrupt junction between high and low Al-composition of AlGaN layers, and a linearly graded AlGaN layer forming a 3 dimensional electron gas (3DEG) profile with 5~6 nm of vertical channel depth which enables the transconductance tailoring. A tailored gm and device scaling are essential to have linearly operating devices and very high frequency operation while maintaining efficiency. Although conventional HEMT structures have been successfully scaled down, the modification of its gm-Vgs profie presents significant challenges. Channel doped metal-semiconductor FETs (MESFETs) and polarization-doped FETs (PolFETs) showed tailored gm-Vgs characteristic, however, they do not lend themselves to device scaling-down with maintaining high carrier density. The new polarization-induced graded AlGaN/GaN HEMT adopts advantages of both HEMT (high scaling factor) and PolFET structure (gm tailoring). The graded-channel and conventional HEMTs are discussed. The polarization-induced 3-D channel is formed by adding a linearly graded layer (from GaN(bottom) to Al0.15Ga0.85N(top) over 5nm) into the conventional HEMT structure. The processing technology including the gate-recess process (12nm of the etch depth) for a conventional Ga-polar AlGaN/GaN HEMTs is used for both devices. The devices fabricated were 150 µm wide, 1.5 µm of the gate length and 4 µm of the source-drain spacing. These devices gave Id,max and peak extrinsic gm of 720 mA/mm and 159 mS/mm, respectively, for the conventional HEMT and 970 mA/mm and 168 mS/mm, respectively, for the graded-channel HEMT. However, the graded-channel HEMT maintains a flat gm value (~155mS/mm) over the wide output current range (0.1~0.9 A/mm) while the gm of conventional HEMT immediately degrades after reaching its peak value. To measure the large signal source resistance (Rs) for extracting the intrinsic gm and the gate-channel bias (Vgc), we introduce a new method fitting the gate-source turn-on bias of transistor (3-teminal) into the one of the gate-source diode (2-terminal). The Rss for the graded-channel and the conventional HEMTs were extracted as 3 Ω-mm and 4.8 Ω-mm, respectively. The intrinsic gms (gmi = gm/(1-Rsgm)) and the electron velocities are estimated from measured gm, Rs and C-V. The peak gmi and electron velocity values are found 675 mS/mm and 1.1x107 cm/s, respectively, for the conventional HEMT, and 321 mS/mm and 0.55 x107 cm/s, respectively, for the graded-channel HEMT. The flattened gmi and electron velocity profile are also found in the graded-channel HEMT. However, the small signal source resistance (rs) is under-estimated due to a relatively long Lg that limits the electron velocity and gmi for the graded-channel.