  By combining angle-resolved photoemission spectroscopy and quantum
oscillation measurements, we performed a comprehensive investigation on the
electronic structure of LaSb, which exhibits near-quadratic extremely large
magnetoresistance (XMR) without any sign of saturation at magnetic fields as
high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal
hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center $\Gamma$ and one
ellipsoidal electron FS at the BZ boundary $X$. The hole and electron carriers
calculated from the enclosed FS volumes are perfectly compensated, and the
carrier compensation is unaffected by temperature. We further reveal that LaSb
is topologically trivial but share many similarities with the Weyl semimetal
TaAs family in the bulk electronic structure. Based on these results, we have
examined the mechanisms that have been proposed so far to explain the
near-quadratic XMR in semimetals.
