What version of Mac OS X are you running?
The kernel_task in Mac OS X 10.9 Mavericks takes 1.07 GB of RAM on my 2012 MacBook Pro (non-Retina) with Intel HD4000 integrated graphics and 16GB of system RAM. Yes, this is completely necessary. If you have more physical RAM, then Mac OS X will use a lot for kernel_task in order to make the system run optimally.
With each new version of Mac OS X over the years, the kernel_task has taken more and more memory to run Mac OS X.
In my experience, if you are running Mac OS X 10.8 Mountain Lion, your Mac needs to have more than 4GB of system RAM to run optimally (without the OS needing to use the swapfile on the hard disk constantly, which degrades performance speed). It now appears that your Mac needs more than 6GB RAM to run Mac OS X 10.9 Mavericks effectively.
The amount of RAM needed for Microsoft Windows 8.0 and 8.1 are comparable. This is simply what is required for the newest personal computer operating systems in 2013.
Please note that many system functions run under kernel_task, and the list of what is running on your Mac changes based on what you are using your Mac for.
I found a good explanation for you, in "Kernel_task taking up RAM in OS X" from CNet in 2011. A quote:
...you will see another process called "kernel_task" that also will
regularly use a few hundred megabytes of real RAM and seem to increase
its RAM footprint with system usage.
The kernel in OS X is the
software architecture that is responsible for handling resources that
processes and programs need. These include the management of
multitasking scheduling, virtual memory, system input and output, and
various communication routines between processes. In addition, the
kernel can be modified and given enhanced functionality by loading
kernel extensions (kexts) to supply system-level management of
features like Bluetooth and Wi-Fi, graphics processors, third-party
hardware, access to peripheral devices, and special filesystem
support. In essence, the kernel is responsible for running your
hardware and making the hardware resources available to applications
and system services.
...the process "kernel_task" may take up a large amount of
system memory. When the system starts up, even
though you may have kernel extensions loaded, not all of the services
are active. The system may be ready to use them, but will not load
them fully until needed. Therefore, if you initially start up your
system and check Activity Monitor, you may see the kernel_task process
taking up a relatively small amount of RAM. When you then start using
your system and activating features like your iSight camera, Wi-Fi
services, switching GPUs, and using external devices, then the
kernel_task will make use of the resources for these devices and will
grow in size.
A reboot seems to clear my system that experiences similar RAM allocation for the kernel, but it will climb up again over time. I have chatted with Apple support and they suggested an SMC reset, which I did along with a PRAM reset and so far, it seems to be under control. It's hovered just under 1GB as I've been working, and watched it dip down a couple of times when some apps were idle.
Long term, resetting SMC & PRAM didn't affect the memory allocation and I've tracked the insane memory usage to the "installd" process.
Open Activity Monitor and FORCE QUIT that process and watch the kernel usage drop down to normal levels. Unfortunately, you have to do this after every startup as it appears to be leaking memory on builds lower than 10.9.1 and 13B42.
Best Answer
Sometimes the RAM doesn't clear properly - try running "purge" from the terminal - this will (as close as possible) clear the inactive RAM for you.
Also, the more RAM you have, the more your computer will use when idle for the background processes. This is normal and it won't get in the way of your performance.