  We study the suprathermal electron acceleration mechanism in a perpendicular
magnetosonic shock wave in a high Mach number regime by using a
particle-in-cell simulation. We find that shock surfing/surftron acceleration
producing the suprathermal electrons occurs in the shock transition region
where a series of large amplitude electrostatic solitary waves (ESWs) are
excited by Buneman instability under the interaction between the reflected ions
and the incoming electrons. It is shown that the electrons are likely to be
trapped by ESWs, and during the trapping phase they can be effectively
accelerated by the shock motional/convection electric field. We discuss that
suprathermal electrons can be accelerated up to $m_i c^2 (v_0/c)$, where $m_i
c^2$ is the ion rest mass energy and $v_0$ is the shock upstream flow velocity.
Furthermore, some of these suprathermal electrons may be effectively trapped
for infinitely long time when Alfv\'en Mach number $M_A$ exceeds several 10,
and they are accelerated up to the shock potential energy determined by the
global shock size.
