  In the current paper, we consider the following parabolic-elliptic semilinear
Keller-Segel model on $\mathbb{R}^{N}$, \begin{equation*} \begin{cases}
u_{t}=\nabla\cdot (\nabla u-\chi u\nabla v)+a u -b u^2, \quad
x\in\mathbb{R}^N,\,\, t>0\cr 0=(\Delta- I)v+ u, \quad x\in\mathbb{R}^N,\,\,
t>0, \end{cases} \end{equation*} where $ \chi >0, \ a\ge 0,\ b> 0$ are constant
real numbers and $N$ is a positive integer. We first prove the local existence
and uniqueness of classical solutions $(u(x,t;u_0),v(x,t;u_0))$ with
$u(x,0;u_0)=u_0(x)$ for various initial functions $u_0(x)$. Next, under some
conditions on the constants $a, b, \chi$ and the dimension $N$, we prove the
global existence and boundedness of classical solution
$(u(x,t;u_0),v(x,t;u_0))$ for given initial functions $u_0(x)$. Finally, we
investigate the asymptotic behavior of the global solutions with strictly
positive initial functions or nonnegative compactly supported initial
functions. Under some conditions on the constants $a, b, \chi$ and the
dimension $N$, we show that for every strictly positive initial function
$u_0(\cdot)$, $$\lim_{t\to\infty} \sup_{x\in\mathbb{R}^N}
\big[|u(x,t;u_0)-\frac{a}{b}|+|v(x,t;u_0)-\frac{a}{b}|\big]=0,$$ and that for
every nonnegative initial function $u_0(\cdot)$ with non-empty and compact
support ${\rm supp}(u_0)$, there are $0<c_{\rm low}^*(u_0)\leq c_{\rm
up}^*(u_0)<\infty$ such that $$\lim_{t\to\infty} \sup_{|x|\leq ct}
\big[|u(x,t;u_0)-\frac{a}{b}|+|v(x,t;u_0)-\frac{a}{b}|\big]=0\quad \forall\,\,
0<c<c_{\rm low}^*(u_0)$$ and $$\lim_{t\to\infty}\sup_{|x|\geq ct}
\big[u(x,t;u_0)+v(x,t;u_0)\big]=0\quad \forall\,\, c>c_{\rm up}^*(u_0).$$
