GPU overheat due to thermal paste

Today I changed thermal pad on my GPU to Arctic Silver 5 thermal paste. After that I checked the temperature in SpeedFan. At first it showed ~90, then 0, then 230 Celsius. After seeing 230 I switched my laptop off. The same paste is on CPU and it stays on 40 Celsium.

Could it be a glitch or my gpu is melting?

EDIT: I couldn't tell how how the heatsink was, but I could feel warm when I put my finger close to it. Not the heatsink though, it's kind of metalic frame on the other side of motherboard around GPU and CPU area.

A laptop GPU can easily be about 90°C and more. But most likely it's a glitch in SpeedFan because it's very seldom that you can read the temperature from a gpu and more seldom when it's a laptop. If you want to be sure you can check it yourself and dump the embedded controller and try to find out the value that stores the temperature. A good utility to work with is the RW tool. But you can also try a demanding benchmark like Furmark and then wait until the laptop overheat and run a thermal shutdown. Most likely a thermal shutdown happens because the cpu is too hot and not the gpu. I've similar temperatures and cleaning my laptop fan is a ritual and my laptop is still working and is over 3 years old.

A GPU temperature of 90C is worrisome. Into the hundreds and it would likely instantly fail. 230C is nearly hot enough to melt tin and you would definitely have smelled something burning. I doubt highly that your GPU reached that real temperature. To be sure, you might want to carefully clean and then reapply the thermal paste to the GPU being careful to make an even, thin covering over the entire chip.

I believe your heatsink is not touching your GPU since you replaced the thermal pad with paste.

A pad ensures there is heatsink to surface connectivity for heat transfer.

I'd advise re-adding the thermal pad back.