This paper contributes to the evaluation of discretization schemes for
the semiconductor device continuity equation. A simple model problem
is described which provides a test any discretization scheme on simpli
cial grids must pass. Otherwise the scheme will fail to compute the mi
nority charge densities in simulation problems. Many schemes published
in literature do not pass this test (e. g. [1], [4], [5], [7], and [8
]). In a last section the relevance of the model problem to realistic
devices is explained.