  Very strong magnetoresistance and a resistivity plateau impeding low
temperature divergence due to insulating bulk are hallmarks of topological
insulators and are also present in topological semimetals where the plateau is
induced by magnetic field, when time-reversal symmetry (protecting surface
states in topological insulators) is broken. Similar features were observed in
a simple rock-salt-structure LaSb, leading to a suggestion of the possible
non-trivial topology of 2D states in this compound. We show that its sister
compound YSb is also characterized by giant magnetoresistance exceeding one
thousand percent and low-temperature plateau of resistivity. We thus performed
in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance,
and Shubnikov--de Haas effect measurements, which reveals only
three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance
data accounts very well for its low-temperature upturn behavior. The
field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding
effective mass anisotropy perfectly agreeing with electronic structure and
quantum oscillations analysis, thus providing further support for 3D-Fermi
surface scenario of magnetotransport, without necessity of invoking
topologically non-trivial 2D states. We discuss data implying that analogous
field-induced properties of LaSb can also be well understood in the framework
of 3D multiband model.
