If you want the Google functionality of Android 4.1.2 Jelly Bean without having to buy the latest Nexus phone, then you're in luck. Thanks to XDA Developers member Faryaab, we can now take advantage of the Nexus experience via the SuperNexus ROM.

Built from Google's AOSP source, SuperNexus gives you the best possible vanilla Android experience you need on your Samsung Galaxy S3 GT-I9300. The ROM is light and has no third-party apps. It is rooted, fully deodexed, and has zero bloatware. It also includes the official Jelly Bean boot animation and many other juicy features.

Since SuperNexus is based on AOSP, you might encounter several problems. First, connecting to Wi-Fi or Wi-Fi tethering may be a challenge. Second, the camera might not be very stable and might force close when you try using the flash. Lastly, the ROM has compatibility issues with exFAT-formatted SD cards. However, these are little sacrifices for a deliciously vanilla Android interface.

This guide shows you how to flash the SuperNexus ROM for the Galaxy S3 I9300.

Warning

• The instructions in this guide are intended for use with the Samsung Galaxy S3, model number GT-I9300. Applying these instructions on another device or model may produce undesired outcomes.
• The information in this guide is provided for instructional and educational purposes only. There is no guarantee that these instructions will work under your specific and unique circumstances.
• Use these instructions at your own risk. We shall not hold any responsibility or liability for whatever happens to you or your device arising from your use of the info in this guide.
• Read and understand the whole guide first before actually performing the instructions.

Requirements

• Samsung Galaxy S3 GT-I9300 with ClockwordMod Recovery installed.
  • To install CWM Recovery, check out our guide on how to install ClockworkMod Touch Recovery 6.0.1.0 on Galaxy S3 I9300.
• Download the following to your computer:
  • SuperNexus I9300 BUILD 5 (SuperNexus-I9300-BUILD5-20121017.zip, md5sum: 60619CFD5989315E15826C2B4A8B6512)
  • GApps (Google Apps) package (gapps-jb-20121011-signed.zip, md5sum: 4e9e7ec3c22b0b3471bd05d62b8a659d)
    • Google Apps JB 11-10-12
    • Alternative Link
• Make sure your device's battery still has at least 70% power. You don't want the device to shut down in the middle of the procedure.
• Backup all personal data on your phone to make sure you have a copy of your personal data (e.g., contacts, SMS, MMS, Internet settings, Wi-Fi passwords, and the like) in case the procedure in this guide erases such data.
  • For backup tips, check our guides on how to sync your data to the cloud and how to create local backups of your mobile data.

Instructions

1. Copy the SuperNexus-I9300-BUILD5-20121017.zip file and the gapps-jb-20121011-signed.zip file to your phone's internal SD Card.
2. Turn your Galaxy S3 off.
3. Boot your phone to Recovery Mode by holding down the Volume Up, Home, and Power button at the same time until recovery boots.
4. Select Wipe data/factory reset > Yes.
5. Once you're done, flash the SuperNexus-I9300-BUILD5-20121017.zip file. Select Install ZIP from SD card > Choose ZIP from SD card. Select the SuperNexus-I9300-BUILD5-20121017.zip file and confirm that you want to install the file.
6. Repeat step 5 and flash the gapps-jb-20121011-signed.zip file.
7. Select Go back > Reboot system now.

Congratulations! You have successfully flashed the SuperNexus ROM to your Samsung Galaxy S3 GT-I9300. You can now enjoy the Nexus experience on your Galaxy S3.