ECS MCP61M-M3 Chipset gets hot when Graphics card is pluged

[caspian]

Dear Forum Members,

I have an ATX mainboard: ECS MCP61M-M3 with CPU: Sempron 140 and Chipset: MCP61.
If I use only the Onboard Graphics, the Chipset's temperature is about 52'C.
If I use a PCIE x16 Graphics Card, the Chipset's temperature is about 70'C and tends to go higher. But the Graphics Card's temperature is normal.
In both the two cases, the PC works fine.
I have tested two different Graphics cards and it gets hotter with both of them.
Any idea why it gets hotter with Graphics Card?

Thanks