I had a customer that recently reached out asking how they could easily audit their entire ESXi infrastructure to determine which hosts was still booting using the legacy BIOS firmware, which has been deprecated and will be removed in a future vSphere release, in favor of the industry standard UEFI firmware type.

In vSphere 8.0 Update 2, a new vSphere API property called firmwareType was introduced and added to the ESXi Hardware BIOS info object that makes it very simple to retrieve with the following PowerCLI 1-Liner:

(Get-VMHost).ExtensionData.Hardware.BiosInfo

Here is an example output for an ESXi host booting with UEFI firmware:

Here is an example output for an ESXi host booting with BIOS firmware:

Since this vSphere API property was recently introduced in vSphere 8.0 Update 2, if you attempt to use this on an ESXi host that is not running 8.0 Update 2, then you will see the field being blank if you are using a newer release of PowerCLI that understands this new property or it will simply not show if you are using an older version of PowerCLI.

Alternatively, if you still need to retrieve this information, you can go directly to ESXi host via SSH, not ideal but you can use the following VSISH command to retrieve this exact information:

vsish -e get /hardware/firmwareType