  Semiconvection - mixing that occurs in regions that are stable when
considering compositional gradients, but unstable when ignoring them - is shown
to have the greatest potential impact on main sequence stars with masses in the
range 1.2 - 1.7 solar masses. We present the first stellar evolution
calculations using a prescription for semiconvection derived from extrapolation
of direct numerical simulations of double-diffusive mixing down to stellar
parameters. The dominant mode of semiconvection in stars is layered
semiconvection, where the layer height is an adjustable parameter analogous to
the mixing length in convection. The rate of mixing across the semiconvective
region is sensitively dependent on the layer height. We find that there is a
critical layer height that separates weak semiconvective mixing (where
evolution is well-approximated by using the Ledoux criterion) from strong
semiconvective mixing (where evolution is well-approximated by using the
Schwarzschild criterion). This critical layer height is much smaller than the
minimum layer height expected from simulations so we predict that for realistic
layer heights, the evolution is nearly the same as a model ran with the
Schwarzschild criterion. We also investigate the effects of compositional
gradient smoothing, finding that it causes convective cores to artificially
shrink in the absence of additional mixing beyond the convective boundary.
Layered semiconvection with realistic layer heights provides enough such mixing
that stars will still evolve as if the Schwarzschild criterion is employed.
Finally, we discuss the potential of detecting such semiconvection and its
implication on convective core sizes in solar-like oscillators.
