The objective of this numerical work is to evaluate the first law and second law performances of a hybrid nanofluid flowing through a liquid-cooled microchannel heatsink. The water-based hybrid nanofluid includes the Fe

3

O

4

and carbon nanotubes (CNTs) nanoparticles. The heatsink includes a microchannel configuration for the flow field to gain heat from a processor placed on the bottom of the heatsink. The effects of Fe

3

O

4

concentration (

φ

Fe

3

O

4

)

CNT concentration (

φ

CNT

) and Reynolds number (

Re

) on the convective heat transfer coefficient

CPU surface temperature

thermal resistance

pumping power

as well as the rate of entropy generation due to the heat transfer and fluid friction is examined. The results indicated higher values of convective heat transfer coefficient

pumping power

and frictional entropy generation rate for higher values of

Re

φ

Fe

3

O

4

and

φ

CNT

. By increasing Re

φ

Fe

3

O

4

and

φ

CNT

the CPU surface temperature and the

thermal resistance decrease

and the temperature distribution at the CPU surface became more uniform. To achieve the maximum performance of the studied heatsink

applying the hybrid nanofluid with low

φ

Fe

3

O

4

and

φ

CNT

was suggested

while the minimum entropy generation was achieved with the application of nanofluid with high

φ

Fe

3

O

4

and

φ

CNT

.