  We report measurements of the inverse squared magnetic penetration depth,
$\lambda^{-2}(T)$, in Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ ($0.115 \leq x \leq
0.152$) superconducting films grown on SrTiO$_3$ (001) substrates coated with a
buffer layer of insulating Pr$_{2}$CuO$_{4}$. $\lambda^{-2}(0)$, $T_c$ and
normal-state resistivities of these films indicate that they are clean and
homogeneous. Over a wide range of Ce doping, $0.124\leq x \leq 0.144$,
$\lambda^{-2}(T)$ at low $T$ is flat: it changes by less than 0.15% over a
factor of 3 change in $T$, indicating a gap in the superconducting density of
states. Fits to the first 5% decrease in $\lambda^{-2}(T)$ produce values of
the minimum superconducting gap in the range of $0.29\leq\Delta_{\rm
min}/k_BT_c\leq1.01$.

Superconductivity