  In this paper, we study the nonconstant positive steady states of a
Keller-Segel chemotaxis system over a bounded domain $\Omega\subset
\mathbb{R}^N$, $N\geq 1$. The sensitivity function is chosen to be $\phi(v)=\ln
(v+c)$ where $c$ is a positive constant. For the chemical diffusion rate being
small, we construct positive solutions with a boundary spike supported on a
platform. Moreover, this spike approaches the most curved part of the boundary
of the domain as the chemical diffusion rate shrinks to zero. We also conduct
extensive numerical simulations to illustrate the formation of stable boundary
and interior spikes of the system. These spiky solutions can be used to model
the self--organized cell aggregation phenomenon in chemotaxis.
