  Using 980 ${\rm fb}^{-1}$ of data {collected} with the Belle detector
operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the
measurements of the masses, and the first measurements of the instrinsic
widths, of the $\Sigma_c(2455)^+$ and $\Sigma_c(2520)^+$ charmed baryons. We
find $M(\Sigma_c(2455)^+)-M(\Lambda_c^+) = 166.17\pm 0.05^{+0.16}_{-0.07}\ {\rm
MeV}/c^2$, $\Gamma(\Sigma_c(2455)^+) = 2.3 \pm 0.3 \pm 0.3\ {\rm MeV/c^2}$,
$M(\Sigma_c(2520)^+)-M(\Lambda_c^+) = 230.9 \pm 0.5 ^{+0.5}_{-0.1}\ {\rm
MeV}/c^2$, and $\Gamma(\Sigma_c(2520)^+) = 17.2^{+2.3\ +3.1}_{-2.1\ -0.7}\ {\rm
MeV}/c^2$, where the uncertainties are statistical and systematic,
respectively. These measurements can be used to test models of the underlying
quark structure of the $\Sigma_c$ states.
