  We present our calculation of D \to pi and D \to K semileptonic form factors
in Nf = 2+1 lattice QCD. We simulate three lattice cutoffs 1/a \sim 2.5, 3.6
and 4.5 GeV with pion masses as low as 230 MeV. The M\"obius domain-wall action
is employed for both light and charm quarks. We present our results for the
vector and scalar form factors and discuss their dependence on the lattice
spacing, light quark masses and momentum transfer.
