  We report on 3.6 cm VLA and VLBA observations of YZ CMi and AD Leo, two
nearby dMe stars. We resolve YZ CMi and can fit a circular symmetrical gaussian
component of FWHP of 0.98 +/-0.2 mas, corresponding to an extent of the corona
above the photosphere of 1.77 x 10^{10} +/-8.8 x 10^{9} cm or 0.7 +/-0.3 Rstar
(Rstar refers to the photospheric radius). We obtain an estimate of the
brightness temperature of 7.3 x 10^{7} K, which is consistent with that
expected from gyrosynchrotron emission. For AD Leo the emitting region is
unresolved. We therefore set a conservative upper limit to its diameter of 1.8
times the photosphere diameter, which leads to an extent of the corona above
the photosphere of <2.8 x 10^{10} cm or <0.8 Rstar. We compare the radio
emitting dMe stars with measured sizes with the Sun and conclude that these
active stars have much more extended coronal radio emission than the Sun. The
VLBA position of YZ CMi has been found to differ by 32 mas from the positions
calculated from the Hipparcos catalogue. The discrepancy is caused by large
errors in the listed proper motion. An improved value is given.
