SN74LVC1G3157-Q1: Max TJ

It's the same as the storage temperature, 150 °C.

Hey Chia Cheng,

You can calculate it using our FAQ : How to Calculate the Max Junction Temperature of an Analog Switch/Multiplexer. which has a excel calculator linked at the very bottom.

I get a little about 230C under worst case operation (max continuous current, max voltage, max RON at max temp).
In reality, the customer will use the storage temp as Clemens mentioned though since the value the switch will actually see won't heat up the junction during your normal operations. 

Thanks,
rami