We present our study of the dependence of the heavy-to-light semileptonic B decay form factors on the heavy-light meson mass MPS. Simulations are made over a range of the heavy quark mass covering both the charm and bottom quarks using the O(a)-improved clover action at β = 5.9 on a 163 × 40 and 243 × 64 lattice. We find that a weak dependence of form factors on MPS observed in previous studies in the region of charm quark persists up to the region of b quark. The soft relation f0(q2max)= fB/fπ is examined and found to be largely violated.