Bonus Stages are extra, optional mini-games that the player can enter through Star Posts in Sonic 3, Sonic & Knuckles and the complete Sonic 3 & Knuckles games. They are not to be confused with Special Stages, as the objective of Special Stages is to collect Emeralds (and possibly extra lives as well), while Bonus Stages are used to obtain lives, shields and rings.
Sonic the Hedgehog 3
In Sonic 3, the only type of Bonus Stage available is the Gumball Machine stage, accessed by touching a Star Post with at least 50 rings in hand and jumping through the ring of stars that appear above the Star Post. This, as the name suggests, is a large gumball machine like those seen in real-life amusement parks, and is accompanied by fitting music. There are red springs at the bottom that propel the player upwards to begin with, but they fall away after the first use. There are yellow spring pads on the walls, like the ones in Metropolis Zone of Sonic 2, only these ones disappear after the first use as well. Every time Sonic or Tails passes over the handle on the front of the machine, a gumball drops out. The player can choose to drop down and collect them or ignore them and carry on using the spring pads to pass over the handle to turn it. Below is a list of collectible gumballs:
| Colour | Effect |
| Blue | Water Shield |
| Orange | Fire Shield |
| Gold | Lightning Shield |
| Pink | Extra Life |
| Gray | Gives 10 rings |
| Black | The player bounces off these |
| Clear | Nothing |
| Green | Regenerates the springs at the bottom of the stage |
Gumballs have appropriate symbols on them as well. The shield gumballs have a letter B for barrier on them. Pink gumballs are marked with a "1up" symbol and grey gumballs have a ring on the front. Green ones have the letters "REP" on the front, standing for "repeat". After exiting the stage the player will be taken back to the Star Post where the player entered the Bonus Stage. The zone is not reset as it is in Sonic 2.
Sonic & Knuckles
The Gumball Machine stage is replaced with two other kinds of Bonus Stage:
Slot Machine (20 rings in hand)
This combines the slot machines in Casino Night Zone of Sonic 2 and the rotating maze that was the basis for the Special Stages in Sonic 1. This may only require 20 rings to enter, but the player cannot obtain shields in this stage, only rings, lives and continues (continues are worth three lives each but reset the player's score to zero when used). Lives are obtained by having 100 or 200 rings. There is a large slot machine in the middle which awards or deducts rings according to what symbols appear:
3x Bar: 8 Rings
3x Ring: 10 Rings
3x Knuckles: 20 Rings
3x Tails: 25 Rings
3x Sonic: 50 Rings
3x Jackpot: 100 Rings
3x Robotnik: -100 Rings
(Sometimes two rings are awarded for certain combinations)
Having 100 rings or less and getting 3x Robotnik does not result in losing a life and will simply leave the player with no rings. There are also four groups of six rings around the slot machine that sometimes award continues when collected.
Most of the elements in Sonic 1's Special Stages reappear here, with goal signs ending the stage if touched and bumpers scattered throughout. The main difference here is in the outer walls of the stage. They start off as blue blocks, but when touched once, they turn yellow, then pink. Touching a block a third time will turn it into a goal sign and the stage will end if it is touched. The player will be thrown onto a wall of these after leaving the slot machine so minimising the time spent in contact with them is the key to getting the most out of this Bonus Stage.
Magnetic Orbs Stage (50 rings in hand)
This stage is similar to the Gumball Stage of Sonic 3. The stage is a long vertical course with large spheres that the player can launch his/her character off of to ascend the stage. Rings can be collected along the way as well as gumballs, which rise up from small, bright spheres after being touched. These are the same as in the Gumball Stage, but with three differences: Firstly, there are no green "Repeat" gumballs. Secondly, ring gumballs can award just 5 rings at the bottom of the stage but are worth 80 rings at the very top. Black gumballs disappear after bouncing off of them once.
The player is given a head start over a horizontal force field across the stage. After a few seconds this begins to rise, and if it catches the player up, the stage ends. The stage also ends if the player reaches the top of the stage.
Sonic 3 & Knuckles
All three of the above kinds of Bonus Stage were used in the complete game. The player could tell what kind of stage a Star Post will lead to before entering the stage by looking at the color of the stars above the Star Post. The Slot Machine has blue and gold stars, the Gumball Stage has white stars and the Magnetic Orbs stage has white and red stars.