  Silicon carbide (SiC) is a wide bandgap (WBG) semiconductor with promising
applications in high-power and high-frequency electronics. Among its many
useful properties, the high thermal conductivity is crucial. In this letter,
the anisotropic thermal conductivity of three SiC samples: n-type 4H-SiC
(N-doped 1x10^19 cm-3), unintentionally doped (UID) semi-insulating (SI)
4H-SiC, and SI 6H-SiC (V-doped 1x10^17 cm-3), is measured using femtosecond
laser based time-domain thermoreflectance (TDTR) over a temperature range from
250 K to 450 K. We simultaneously measure the thermal conductivity parallel to
(k_r) and across the hexagonal plane (k_z) for SiC by choosing the appropriate
laser spot radius and the modulation frequency for the TDTR measurements. For
both k_r and k_z, the following decreasing order of thermal conductivity value
is observed: SI 4H-SiC > n-type 4H-SiC > SI 6H-SiC. This work serves as an
important benchmark for understanding thermal transport in WBG semiconductors.
